This invention relates to apparatus for controlling the idle speed of an internal combustion engine and more particularly to a vacuum operated unit for obtaining such control.
It is advantageous to control the position at which a carburetor throttle valve is allowed to close when an engine on which the carburetor is mounted is idling. This is because engine idle speed is thus controlled which helps improve both fuel economy and reduce exhaust emissions. Various devices are available for controlling engine idle, among these being the devices shown in U.S. Pat. Nos. 4,067,306 and 4,315,174 both of which are assigned to the same assignee as the present application. The devices shown in these patents as well as the subject of the present application are used in conjunction with an electronic feedback system to achieve idle speed control. In addition to the advantages noted above, use of these devices effectively tamperproofs the idle speed system of the carburetor to prevent adjustment of engine idle speed by modifying the carburetor after it leaves the manufacturers.